1. Field of Invention
The present invention generally relates to magnetic field sensing, and more particularly to a magnetic field sensor device that can be used in both compassing and power switching functions.
2. Description of Related Art
Magnetic field sensors are designed to detect changes or disturbances in magnetic fields. From this initial detection, the sensors are able to derive information on properties such as direction, presence, rotation, angle, or electrical currents. Magnetic field sensing has a variety of applications including navigation, medical diagnostics, surveillance, mechanical component characterization, and detection of minerals, electrical devices, and power lines.
Consumer and non-consumer devices are constantly being updated to include more and more features. Magnetic field sensing is likely to become a part of many of these devices. For example, cell phones will be able to provide compassing functions by including magnetic sensing circuitry in their designs. Cell phones (e.g. flip-style or sliding-style phones) can also use a magnet and magnetic sensor to determine when a user has opened the phone, so that the screen can be powered up. Other consumer devices, such as Personal Digital Assistants (PDAs), portable computers (e.g. notebook computers), and handheld GPS receiver units could similarly make use of magnetic field sensing to provide increased functionality to the user.
For flip-style cell phones, switching typically has been achieved by placing a Hall Effect sensor in one panel of the phone and a permanent magnet in the other panel of the phone. When the phone is closed, the sensor and magnet are in close proximity, such as on top of each other. A voltage is applied to the sensor in such a way that in this closed configuration the Hall voltage is zero and power to the display and/or other components is off. When the phone is opened the sensor and the magnet are no longer in close proximity. Given the same applied voltage in this open configuration, a Hall voltage will be created and power can be switched on (e.g. to light up the screen display).
Magnetic compassing sensors and on/off power switching sensors are typically separate, unintegrated devices. The two sensors are designed to measure different target magnetic fields: the compassing sensors measure the Earth's magnetic field, while power switching sensors measure the close presence of a permanent magnet, for example.
Because size and cost are primary drivers in many consumer devices, a single magnetic field sensor device that combines both magnetic compassing and on/off power switching would be desirable. This device would be able to distinguish between a compassing signal and a power switching signal.